INTENSITY IN RHODE ISLAND REDS 9 



individuals that showed no evidence of broodiness in the first laying year. Hays 

 (1933) stated that 1188 pullets that showed evidence of broodiness had a mean 

 winter clutch size of 2.96 compared with a mean winter clutch size of 2.50 for 

 2679 individuals that gave no evidence of broodiness in their first laying year. 



The present population included 56 pullets that gave evidence of broodiness 

 in the first year and 1414 pullets that failed to show evidence of broodiness in 

 the first laying year. The mean winter clutch size of the broody birds was 3.81 

 compared with 3.20 for the non-broody population. The difference, .61, was 

 tested for significance by Fisher's t method. The value of t was 3.09, which indi- 

 cates that the broody population was definitely superior in winter clutch size. 

 This confirms the previous observation. 



Relation between Intensity in Winter and in the Other Seasons 



14. Winter Clutch Size and Spring Clutch Size 



As already indicated, winter clutch size is measured over the period from first 

 pullet egg to March 1. Spring clutch size may be determ ned for the period 

 March, April, and May, which is the normal hatching season for this area. It 

 is a season when egg production usually stands at a high level and when unim- 

 proved hens usually lay eggs. It is important to know whether winter clutch 

 size and spring clutch size are intimately correlated in our high producing birds. 

 In a previous study (Hays and Sanborn, 1932) using lower producing birds, the 

 correlation ratio was found to be .4171, which is rather intimate. 



The present population included 1467 birds from which the following constants 

 were derived: 



Number of birds 1467 



Mean winter clutch size — eggs 3.23 



Winter clutch size standard deviation + 1.42 



Mean spring clutch size — eggs 4.04 



Spring clutch size standard deviation ± 2.44 



Coefficient of correlation + .4636 + .0138 



Correlation ratio .4864 



The above data show that even in these superior birds spring clutch size was 

 larger than winter clutch size. In other words, environmental conditions of the 

 spring period, March, April, arrd May, stimulated the birds to a new high level of 

 intensity, even though they had been laying at a high rate. Regression was found 

 not to be strictly linear so that the correlation ratio more accurately expresses the 

 association between wmter clutch size and spring clutch size. The correlation 

 ratio was .4864, and its squared value, .24, indicates that about 24 percent of the 

 variation in spring clutch size is due to variation in winter clutch size. Selection 

 on the basis of large winter clutch size is, therefore, a very good criterion of large 

 spring clutch. These data are in agreement with those of Lerner and Taylor 

 (1937) who found an intimate correlation between winter and spring rate in 

 White Leghorns. 



15. Winter Clutch Size and Summer Clutch Size 



Production during the summer months, June, July and August, is very impor- 

 tant in flocks bred for high egg production. Environmental conditions are often 



